Learn Farsi: لطفاً این اسباب‌بازی را نچرخان!

The base verb is charkhidan (to spin or turn), and its present stem is charkh. By adding the causative suffix -ân to this stem, we get the new present stem charkhân (to make something spin). To make it a negative command, we just add the negative prefix na- to the front, giving us nacharkhân.

Could I use the regular negative imperative nacharkh instead?

No, because charkhidan is an intransitive verb; it is used when something spins by itself (like a wheel spinning). Here, you are telling someone to spin an object. When the action is done to a direct object, you must use the causative, or transitive, form charkhândan to mean 'make the object spin'.

Why is the word râ used in this sentence?

The word râ marks the definite direct object. Because the speaker is talking about a specific toy (in asbâb-bâzi / this toy) that receives the action of being spun, râ is required immediately after it to show it is the target of the verb.

How is the word for toy, asbâb-bâzi, constructed?

It is a compound word made of two parts. Asbâb means tools, goods, or stuff, and bâzi means play or game. Put together, it literally means play-stuff or tools for playing.